Short edge management in rule based OPC

ABSTRACT

The invention discloses a method and apparatus for modifying, as appropriate, the geometries of a polygon. Based on various attributes associated with the polygon and its surroundings, modification of the location of the edge segments may conditionally occur. Additionally, if these modifications occur, a method to minimize the introduction of short edges during the modification is provided.

FIELD OF THE INVENTION

The present invention relates to the field of electronic designautomation software. More specifically, the invention relates to theautomatic adjustment of layout of integrated circuit designs.

BACKGROUND OF THE INVENTION

To be able to continually increase the gate count of semiconductordevices on fixed die size, integrated circuit (IC) designs have involvedshrinking feature sizes. For the next decade, the outlook is strong forphotolithography to continue to be the process by which IC aremanufactured. When processing the features in today's deep sub-micronprocesses, the wavelength of light used in the photolithography processis less than that of the feature size. A result of the use ofphotolithography under these “tight” conditions is that the resultingdesign, notwithstanding the use of phase shift masking, does notprecisely match the desired design.

A method of automatically correcting the resulting differences involvesmaking subtle modifications to the mask or reticle used in thephotolithography process (hereinafter collectively referred to as mask).These modifications are termed optical proximity corrections or opticaland process corrections. Whether the term is referring to opticaldistortions alone or for process distortions in addition to opticaldistortions determines which term is the proper term to use. Regardlessof the reason for these corrections, the discussions herein willgenerically refer to either or both of these types of corrections asOPC.

There are two basic types of OPC, rule-based and model-based. Rule basedOPC applies corrections to the mask based on a predetermined set ofrules. Thus, if an analysis of the mask determines that the mask meets apredetermined set of conditions, a process applies the appropriatecorrection to the mask for the conditions met. The corrections resultingfrom the rule-based approaches are typically less accurate, whencompared to model based correction. However, rule-based corrections aremore computationally efficient, and less costly. In contrast, amodel-based OPC technique uses process simulation to determinecorrections to the masks. The model-based OPC corrections, generated inaccordance with the results of these simulations, generally provide forgreater accuracy than the corrections provided by rule-based OPC.However, model-based OPC is computationally intensive and therefore timeconsuming as well as costly.

SUMMARY OF THE INVENTION

The invention discloses a method and apparatus for modifying, asappropriate, the geometries of a polygon. Based on various attributesassociated with the polygon and its surroundings, modification of thelocation of the edge segments may conditionally occur. Additionally, ifthese modifications occur, a method to minimize the introduction ofshort edges during the modification is provided.

In one embodiment of the present invention, if the spacing between anedge segment and the nearest feature outside of a polygon comprising theedge segment is below a certain threshold, the edge segment will benegatively biased.

In one embodiment of the present invention, if the length of an edgesegment, as a result of biasing, is too short as compared to a referencevalue, the edge will be lengthened by shortening adjacent edge segmentsand lengthening the short edge segment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1—A flowchart of process flow of one embodiment of the presentinvention.

FIG. 2—A sample polygon layer to which the flowchart of the embodimentof FIG. 1 is applied.

FIG. 3—A resulting polygon layer from the application of the processembodiment of the FIG. 1 to the sample polygon layer of FIG. 2.

FIG. 4—A more complex correction based on additional dimensions.

FIG. 5—A table approach to correction of edge placement.

FIG. 6—A polygon with no correction.

FIG. 7—The polygon of FIG. 6 with 2-dimensional bias correction applied.

FIG. 8—The polygon of FIG. 7 with 3-dimensional bias correction applied.

FIG. 9—The 2-dimentional table applied to the polygon of FIG. 6establishing the bias shown in FIG. 7.

FIG. 10—A 3-dimentional table applied to the polygon of FIG. 6establishing the bias shown in FIG. 8.

FIG. 12—An example partial layer of polygon showing width and spacing towhich an embodiment of this invention may be applied.

FIG. 13—A 2-dimensional table of correction, in accordance with oneembodiment, to be applied to the example partial layer polygon of FIG.12.

FIG. 14—The resulting polygon from the application of the table ofcorrection of FIG. 13 to the example partial layer polygon of FIG. 12.

FIG. 15—Resulting polygon from a space-priority based bias.

FIG. 16—Example violation of minimum edge length during rule based OPCcorrection.

FIG. 17—Results of applying short edge corrections to rule based OPC.

FIG. 18—An example computer incorporated with an embodiment of thepresent invention.

FIG. 19—An Electronic Design Automation (EDA) Tool Suite incoporatedwith the teachings of the present invention.

FIG. 20—A networking environment suitable for practicing the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, various aspects of the present inventionwill be described. For purposes of explanation specific numbers,materials and configurations are set forth in order to provide athorough understanding of the present invention. In some instances,well-known features are omitted or simplified in order not to obscurethe present invention.

Various operations will be described as multiple discrete steps, in amanner that is most helpful in understanding the present invention,however, the order of description should not be construed as to implythat these operations are necessarily order dependent. In particular,these operations need not be performed in the order of presentation.Further, the description repeatedly uses the phrase “in one embodiment”,which ordinarily does not refer to the same embodiment, although it may.

Width and Space Based OPC

FIG. 1 shows a flowchart of a layout correction process in accordancewith one embodiment of the present invention. This flowchart depicts aprocess for applying rules that advantageously determine whether toapply a correction to an edge segment corresponding to a portion of aline segment defining a side of a polygon. This polygon typicallyrepresents a feature on a layer of a design of an integrated circuit.The rules are based on the width of the polygon at the portion of theedge segment and the spacing between the portion of the edge segment ofthe polygon and the nearest structure. FIG. 3 shows the resultingpolygons with at least one edge segment of Poly1 modified when theprocess of FIG. 1 is applied to the polygon structure of FIG. 2.

In this embodiment of the invention, each side of each polygon in alayer is processed. Each side of a polygon is processed as a linesegment, and each line segment of a polygon is further divided into oneor more edge segments 110. Thus, an edge segment is at least a portionof a line segment (or side) of a polygon. Various embodiments of theinvention determine which portion of the line segment defines an edgesegment.

In one embodiment of the invention, the method ascertains which portionof a line segment defines an edge segment by determining at least twoattribute sets along the line segment. The first attribute set is thespacing distances between the various portions of the line segment andtheir corresponding closest neighboring structures outside the polygon.The second attribute set is the widths of the polygon for the variousportions of the line segment. That is, the distance from the variousportions of the line segment to corresponding portions of a line segmentor segments on the opposite side of the polygon. An edge segment will bea contiguous portion of the line segment where each of these twoattributes remains constant. In other words, when continuing on the linesegment, if either the width of the polygon or the spacing between thepolygon and another outside structure changes, then this signals thebeginning of a new edge segment.

FIG. 2 shows an example of dividing a side, or line segment, of apolygon into edge segments. The “bottom” side of Poly1 is divided by thepresent embodiment of the invention into the four edge segments asshown, edge segments 210-216 in FIG. 2. In this example, the width ofPoly1 is constant (0.30) so any division of the bottom edge of Poly1 ismade based on spacing between the various portions of the line segmentand the corresponding nearest neighboring outside structures. Beginningat the bottom right corner, the spacing between Poly1 and the nextstructure, Poly3, is 0.7. In determining the edge segment definition,one continues along the bottom edge until either the space or the widthattribute changes. In this example, this condition occurs at point 226.The portion of the edge from the corner to this point 226 defines edgesegment 216. Continuation of this process for the remaining portions ofthe bottom edge of Poly1 results in the definition of edge segments210-216.

In this embodiment of the present invention, during processing of anedge segment, the spacing between the edge segment and an outsidenearest neighboring structure of the polygon, with respect to the edgesegment currently being processed, is compared to a reference value 120.In the example shown in FIG. 1, the reference value is 0.25 units. Ifthe spacing is not below the reference value of this embodiment, thenthe process does not modify the edge segment, and the next edge segmentis processed. If however, the spacing is less than the reference value,in this case 0.25, the process further checks the width of the polygonalong the edge segment currently being processed. If the width of thatpolygon is above a certain reference value, in this case 0.27, then theprocess reduces the width of the polygon at the edge segment by 0.01units. This reduction in the width is phrased as a negative bias,whereas an increase in the width of a polygon is phrased as a positivebias.

As previously mentioned, the application of the process in FIG. 1 to thepolygon structures of FIG. 2 results in the modified polygon structuresshown in FIG. 3. In processing the polygon structure of FIG. 2, pursuantto the process of FIG. 1, only edge segments 218 and 212 result inaffirmative responses to queries 120 and 130 of FIG. 1. As a result,these are the only two edge segments which have biases correspondinglyapplied to them. In each case, the bias applied is a −0.01, and theresulting edge segments are shown in FIG. 3. The width of Poly1 at edgesegment 312 is reduced to 0.29. Similarly, the width of edge segment 318in Poly2 is also reduced to 0.29.

In one embodiment, the processing and the bias applications arealgorithmically effectuated, whereas in another embodiment, a table ispreferentially employed.

FIG. 4 shows an example pseudocode for the handling of edge segments ofa layer based on a slightly more complicated scheme than that shownabove. The bias to an edge segment, as shown in FIG. 4, varies greatlyin this embodiment of the present invention. In an alternate embodiment,a table that parallels the values of the algorithm is employed instead,as shown in FIG. 5. In one embodiment of the present invention, thetable is implemented via an array data structure. In another embodimentof the present invention, the table is implemented via a hash table andsupporting functions.

By utilizing a table-based approach, each edge segment can bebucketized. That is, each edge segment can be placed in a bucket thatcorresponds to a unique cell entry in a table. Thus each bucket may haveany number of edge segments that have attributes that match therequirements of each cell. For example, using the embodiment shown inFIG. 5, all edges with (0.4<spacing<=0.7) and (0.2<=width<0.3) will fallinto a bucket corresponding to cell 510. Thus, in one embodiment of thepresent invention, as the edges are processed by the present invention,when it is determined that an edge's bias should be changed, it ismerely moved to a different bucket. In this manner, the edges are notimmediately biased, the biases are performed at the end of theprocessing of the determination of each bias. This approachadvantageously reduces the processing time vis-á-vis an embodiment whereeach edge is biased as the appropriate biased is determined.

Additional Dimension OPC Approach

Where more granularity of edge segment adjustment is needed vis-á-vis atwo-dimensional approach, embodiments of the present invention mayemploy other dimensions, in addition to width and spacing, indetermining the appropriate bias values. In one embodiment of thepresent invention, the length of the polygon at the edge segmentundergoing processing is also used to determine the proper bias value.The length of the polygon in such an embodiment is the same as thelength of the edge segment. For example, FIG. 6 shows a polygon witheight sides. Each side comprises a single edge segment except the bottomside whose length is 1.0 but which is comprised of 3 edge segments 670,610, 680, of 0.28, 0.40 and 0.32 length, respectively. Thus, in thisembodiment, when processing the three edge segments, these individuallengths of the polygon at the edge segment only will be used indetermining the OPC bias value vis-á-vis the length of the entire side.

FIG. 9 shows a table which applies a bias to edge segments based on twoattributes of the edge segment, the width of the polygon at the edgesegment and the distance of the edge segment from the nearestneighboring structure outside the polygon. Assuming the nearestneighboring structure to the edge segment of the polygon in FIG. 6 isgreater than 0.7, FIG. 7 shows a resulting polygon with edge segments ofFIG. 6 biased via the bias values as set out in the table of FIG. 9. Thetwo 710 edge segments are biased for a positive 0.02 units based on theproper determination from table of FIG. 9. Note that other edge segments720-750 on the polygon are biased by the same amount by applying thetwo-dimensional bias rules. The biasing that occurs is performed withrespect to the width of the polygon and the spacing to the nearestneighboring structure outside the polygon. The biasing does not accountfor any extra dimensions such as length of the edge segment beingprocessed by the present embodiment.

FIG. 8 shows the polygon from FIG. 6 biased via another embodiment ofthe present invention. This embodiment of the invention uses anadditional dimension of length to ascertain the correct bias value. FIG.10 shows a portion of a table used to determine the proper biases forthis embodiment. Refer now to edge segment 820 in FIG. 8. The widthmeasurement for this edge segment, as shown in FIG. 8, is 1.0 and thelength measurement for this segment is 0.2. Note in the table in FIG. 10at row 1020, that when the length value is less than 0.3, the bias valueis to be 0.0. For edge segments 810, the length of these edge segmentsis 0.4, with the width being 0.35. As a result, these edge segments willbe biased by 0.2 as detailed in the table in FIG. 10 at row 1010. Theresultant polygon structures are shown in FIG. 8.

Another embodiment of the present invention takes into account a secondlength value in determining bias for edge segments. FIG. 11 showsanother set of polygons. A first polygon 1110 has an edge with arelatively long length L1. A second polygon 1120 has an edge with arelatively short length L2 1125 below some reference length Lref (notshown). In this embodiment of the invention a user specifics a secondlength such that when an edge segment of a layer under consideration forbiasing 1115 is referencing another polygon with an reference edge 1125whose length is below a minimum reference length Lref, then no biasingof the edge segment under consideration will occur. This may bedesirable where users do not want narrow line-end edges to be used fordetermining the spacing measurements. In another embodiment of theinvention, the edge segment under consideration for biasing 1115 isstill biased, notwithstanding the proximity of the short edge, but thebias value is attenuated as a function of the length of the second edgesegment 1125.

Short Edge Interdiction

When performing biasing as discussed above, it is likely that differentedge segments may be biased by different values. This can result inoriginal (input) edge segments that are sub divided into smaller edgesegments. This may result in (1) additional edge segments that (2) maybe smaller than a threshold value. If each additional edge segment issufficiently long so that there is not a problem with themanufacturability of those edges, then it may not be necessary toattempt to rid the design of those additional edges.

However there are times when making adjacent edge biases the same isdesired. This would occur when the introduction of new edge segmentsresults in edge segments below a threshold value. By having edgesegments below a certain value there may be effects on design rules forthe given manufacturing process.

An aspect of the invention is the ability to not allow short edges belowa certain threshold. The present invention can accomplish this byresolving inconsistent biases under certain circumstances. In oneembodiment of the present invention, the inconsistent biases areresolved when one edge segment is below a user specified value. In oneembodiment, the inconsistent biases are resolved when one edge is belowa process specific threshold value. In one embodiment all inconsistentbiases are resolved.

Inconsistent Biases

Edge Merging

Another aspect of the invention is the ability to determine how toresolve adjacent edge segment biases, which may be inconsistent or evenconflicting. For example, when two edge segments are to be biased, whichbias measurement, if any, should an algorithm apply to prohibit theintroduction of additional short edges? FIG. 12 shows a layer withpolygons upon which one embodiment of the present invention operates.The figure also shows measurements of varying widths of polygon B(AA-AC). Additionally, FIG. 12 shows the spacing at different pointsbetween polygons A and B (A-D).

FIG. 13 shows a chart with the bias values that the present embodimentof the invention will apply to an edge segment. Space B and width ABdefine edge segment 1210. Space C and width AB define edge segment 1220.Edge2 is therefore comprised of 2 edge segments 1210 and 1220. Lookingfor the appropriate bias values for the B/AB space/width combination inFIG. 13, it is determined that the bias 1310 for edge segment 1210 is0.2. In contrast, by looking up C/AB in FIG. 13 it is determined thatthe bias for edge segment 1220 is 0.1. This separate application ofdifferent biases to edge segments 1210 and 1220 results in an additionaledge being created, one for each biased edge segment, as shown in FIG.14. The addition of too many extra edges during processing is undesiredbehavior.

Thus, when two biases for adjacent edge segments differ, variousembodiments of the present invention apply a resolution function todetermine the correct bias value to be employed, to avoid introductionof additional edges. This resolution may be performed based on anynumber of criteria. One embodiment of the present invention implements apriority scheme wherein a “maximizing spacing” scheme attempts to applybiases wherein a space-attribute bias determination assumes priorityover a width-attribute bias determination. For example, refer again toFIG. 12, where original spacing at C is 1.35 and the spacing at B is1.75. Applying each of the two possible biases from the table of FIG. 13to both 1210 and 1220 results in spacing values of 1.65 and 1.35 for Band C, respectively, in the case of a 0.1 bias, and 1.55 and 1.25 for Band C in the case of the 0.2 bias. Thus, applying the 0.1 bias valueresults in the maximization of the spacing for both B and C.Accordingly, in the embodiment of the invention with a “maximizingspacing” resolution, the 0.1 bias value is applied, resulting in thecorrected polygon of FIG. 15.

In another embodiment of the present invention, the user may specify themethod of determining the resolution; In yet another embodiment of thepresent invention, rules associated with the process used for the ICfabrication are used to determine what the resolution function will be.

A situation may arise where the weighing of both biases results in a“tie” as determined by the method of the embodiment. In this case, otherapplication dependent heuristics may be employed for tie breaking. Thesemay include choosing a weighted bias or user specified tie breakingrules.

Edge Lengthening

Another option for resolving the occurrence of short edges is to attemptto lengthen edge segment corrections. In one embodiment of theinvention, the length of an edge segment is checked against a minimumedge segment length. If the embodiment determines that the edge segmentdoes not meet the minimum segment length, the embodiment will checkadjacent edge segments to determine their length. If the embodimentestablishes that there is sufficient length in the short edge segmentand the adjacent edge segment combined such that length can be removedfrom the adjacent edge segment and added to the short edge segment,resulting in two edge segments that meet the minimum lengthrequirements, then the edge segments are so modified.

Refer now to FIG. 16 wherein an example of an edge-lengthening situationappears. In this embodiment, a polygon exists 1610 where an originaledge 1620 has modifications based on requirements as previous discussed.Based on criteria, the two edge segments, edge seg1 1630 and edge seg21640 are to replace the original edge 1620. This embodiment of theinvention has a minimum segment length of 0.4. However, the edge seg21640 has a length of 0.2 and is shorter than the minimum segment lengthof 0.4. In this embodiment of the invention, the adjacent segment edgeseg1 1630 will be checked. This segment has a length of 0.8. As aresult, it is possible to modify the length of edge seg2 1640 to meetthe minimum requirement of 0.4 by taking length from edge seg1 1630.

The resulting corrections are shown in FIG. 17. In this figure, edgeseg2 1740 has been extended to meet the minimum length requirement of0.4. There is a shorter edge seg1 1730 reflected in the modificationsmade to allow edge seg2 to meet the minimum requirements.

In one embodiment of this invention, only part of the requirementaddition to an edge segment is taken from a single edge. This results ina short edge that does not meet the minimum requirement, but isnevertheless closer than the original. In one embodiment of the presentinvention, a short edge is between to other edge segments. In thisembodiment “length” is taken from two adjacent edge segments when anedge segment does not meet a minimum length requirement.

User Device Embodiment

Hardware

FIG. 18 illustrates one embodiment of a user apparatus suitable to beprogrammed with the utility application of the present invention. Asshown, for the illustrated embodiment, user device 1800 includesprocessor 1802, processor bus 1806, high performance I/O bus 1810 andstandard I/O bus 1820. Processor bus 1806 and high performance I/O bus1810 are bridged by host bridge 1808, whereas I/O buses 1810 and 1820are bridged by I/O bus bridge 1812. Coupled to processor bus 1806 iscache 1804. Coupled to high performance I/O bus 1810 are system memory1814 and video memory 1816, against which video display 1818 is coupled.Coupled to standard I/O bus 1820 are disk drive 1822, keyboard 1824 andpointing device 1828, and communication interface 1826.

These elements perform their conventional functions known in the art. Inparticular, disk drive 1822 and system memory 1814 are used to storepermanent and working copies of the electronic design system. Thepermanent copy may be pre-loaded into disk drive 1822 in factory, loadedfrom distribution medium 1832, or down loaded from a remote distributionsource (not shown). Distribution medium 1832 may be a tape, a CD, a DVDor other storage medium of the like. The constitutions of these elementsare known. Any one of a number of implementations of these elementsknown in the art may be used to form computer system 1800.

Certain embodiments may include additional components, may not requireall of the above components, or may combine one or more components.Those skilled in the art will be familiar with a variety of alternativeimplementations.

EDA Tool Suite

Refer now to FIG. 19 wherein an EDA tool suite incorporated with a“Short edge management in rule based OPC” module of the presentinvention in accordance with one embodiment is shown. As illustrated,EDA tool suite 1900 includes OPC module 1902 incorporated with theteachings of the present invention as described earlier with respect toFIGS. 1-17. Additionally, EDA tool suite 1900 includes other toolmodules 1904. Examples of these other tool modules 1904 include but arenot limited to synthesis module, DRC module and LVS module.

Remote Client

FIG. 20 shows an embodiment of the present invention 2000 with a remoteclient. In this embodiment, user controls, via a user client 2010,execution of an EDA tool suite 2040 containing a “Short edge managementin rule based OPC” module incorporated with the teachings of the presentinvention. The user interacts with a server 2030 executing the EDA toolsuite 2040 through a network 2020. The server 2030 executes the EDA toolsuite 2040 which reads the user design data 2050, performs operations onuser data 2040 and provides feedback to user via user client 2010. Invarious other embodiments of the present invention the EDA tool suite,user client and user design data can be distributed amount severalnetwork elements.

Conclusion

In the present description, an advantageous method of performing OPC toan IC mask layout as well as a method for managing short edge generationin the layout has been described.

What we claim is:
 1. A method of performing process correction at alayer of an integrated circuit design comprising: determining a width ofa polygon of said layer at an edge segment of said polygon; determininga spacing from said edge segment of said polygon to a neighboringfeature in said layer; determining a length of said edge segment; andconditionally modifying said edge segment based at least in part on atleast a selected one of said width, said length and said spacingdeterminations.
 2. The method of claim 1 wherein said conditionallymodifying said edge segment is based at least in part on exactly one ofsaid width, said length and said spacing determinations.
 3. The methodof claim 1 wherein said conditionally modifying said edge segment isbased at least in part on said length determination.
 4. The method ofclaim 1 wherein said conditionally modifying said edge segment is basedat least in part on said length and said spacing determinations.
 5. Themethod of claim 1 wherein said conditionally modifying said edge segmentis based at least in part on said length, said width and said spacingdeterminations.
 6. The method of claim 1 wherein said conditionalmodification of said edge segment comprises a decrease in said width ofsaid edge segment if said width exceeds a reference width value.
 7. Themethod of claim 1 wherein said conditional modification of said edgesegment comprises an increase in said width of said edge segment if saidspacing exceeds a reference spacing value.
 8. The method of claim 1wherein said conditional modification of said edge segment comprises adecrease in said width of said edge segment if said width exceeds areference width value and said spacing does not exceed a referencespacing value.
 9. The method of claim 1 further comprising determining asecond length of an edge segment of said neighboring feature; andwherein said conditionally modifying said edge segment is based at leastin part on at least a selected one of said width, said length, saidsecond length and said spacing determinations.
 10. The method of claim 9wherein said conditionally modifying said edge segment is based on saidsecond edge segment.
 11. The method of claim 1 wherein a bucketizedapproach is utilized.
 12. An apparatus comprising: a machine readablemedium having stored therein a plurality of programming instructionsdesigned to operate said apparatus to enable said apparatus to:determine a width of a polygon, of a layer of an integrated circuit, atan edge segment of said polygon; determine a spacing from said edgesegment of said polygon to a neighboring feature in said layer;determine a length of said edge segment; and conditionally modify saidedge segment based at least in part on at least a selected one of saidwidth, said length and said spacing determinations; and a processorcoupled to said machine readable medium to execute said plurality ofprogramming instructions.
 13. The apparatus of claim 12 wherein saidprogramming instructions are modified to conditionally modify said edgesegment based at least in part on said length determination.
 14. Amachine accessible medium having stored therein a plurality ofprogramming instructions designed to operate an apparatus to enable saidapparatus to: determine a width of a polygon, of a layer of anintegrated circuit, at an edge segment of said polygon; determine aspacing from said edge segment of said polygon to a neighboring featurein said layer; determine a length of said edge segment; andconditionally modify said edge segment based at least in part on atleast a selected one of said width, said length and said spacingdeterminations.
 15. The machine accessible medium of claim 14, whereinsaid programming instructions are modified to conditionally modify saidedge segment based at least in part on said length determination.